Catalytic hydrocracking

ABSTRACT

Catalytic hydrocracking of polynuclear aromatic containing feedstocks is conducted over catalysts comprising zeolites in intimate contact with a nickel-tungsten hydrogenation component. Said zeolites are characterized by a silica to alumina mole ratio of at least 12, a constraint index within the approximate range of 1 to 12 and an alpha value of between about 25 and 200.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to catalytic hydrocracking. More particularly,this invention is concerned with hydrocracking of polynuclear aromaticcontaining feedstocks with a catalyst exemplified by small crystal sizeZSM-5 associated with nickel-tungsten.

2. Description of the Prior Art

The hydrocracking of hydrocarbons to produce lower boiling hydrocarbons,and in particular, hydrocarbons boiling in the motor fuel range, is anoperation upon which a vast amount of time and effort has been spent inview of its commercial significance. Hydrocracking catalysts usuallycomprise a hydrogenation-dehydrogenation component deposited on a acidicsupport such as silica-alumina, silica-magnesia, silica-zirconia,alumina, acid treated clays, zeolites and the like.

Crystalline zeolites have been found to be particularly effective in thecatalytic hydrocracking of a gas oil to produce motor fuels and such hasbeen described in many U.S. patents including Nos. 3,140,249; 3,140,251;3,140,252; 3,140,253; and 3,271,418.

A catalytic hydrocracking process utilizing a catalyst comprising azeolite dispersed in a matrix of other components such as nickel,tungsten and silica-alumina is described in U.S. Pat. No. 3,617,498. Ahydrocracking catalyst comprising a zeolite and ahydrogenation-dehydrogenation component such as nickel-tungsten-sulfideis recited in U.S. Pat. No. 4,001,106. In U.S. Pat. No. 3,758,402, ahydrocracking process is disclosed wherein the catalyst comprises alarge pore zeolite such as zeolite X or Y and a smaller pore zeolitesuch as ZSM-5 which may have a hydrogenation/dehydrogenation componentsuch as nickel-tungsten associated with at least one of the zeolites.Hydrocarbon conversion utilizing a catalyst comprising a zeolite, suchas ZSM-5, having a zeolite particle diameter in the range of 0.005micron to 0.1 micron and in some instances containing ahydrogenation/dehydrogenation component is related in U.S. Pat. No.3,926,782. The hydrocracking of lube oil stocks employing a catalystcomprising hydrogenation components and a zeolite such as ZSM-5 isdisclosed in U.S. Pat. No. 3,755,145.

Whereas a great amount of attention has been given to hydrocrackingpetroleum gas oils, much less emphasis has been devoted to hydrocrackingpolynuclear aromatic containing feedstocks such as FCC cycle oils andcoal derived liquids. Such polynuclear aromatic stocks requiresaturation and thus increased hydrogen consumption during processing inorder to produce a suitable liquid product. U.S. Pat. No. 3,523,886discloses a process for making liquid fuel from coal by solventextraction which involves catalytic hydrocracking.

Hydrocracking generally requires a clean feedstock, or alternatively,due to the large heteroatom content of many feedstocks, hydrocrackingfrequently must be preceded by a pretreatment stage. It would be veryadvantageous to have a system which would be able to both pretreat andhydrocrack in one operation.

SUMMARY OF THE INVENTION

It has now been discovered that catalytic hydrocracking of polynucleararomatic containing feedstocks can advantageously be conducted bycontacting said feedstocks and hydrogen under conversion conditions witha catalyst comprising a zeolite having an alpha value of between about25 and 200 in intimate contact with a nickel-tungsten hydrogenationcomponent. Said zeolite is characterized by a silica to alumina moleratio of at least 12, a constraint index in the approximate range of 1to 12.

Hydrocracking in accordance with this invention results in reducing thenitrogen content and the sulfur content of the feedstock, whileincreasing the hydrogen content and converting a substantial amount ofthe polynuclear aromatics to saturates, monoaromatics and gasoline. Thenitrogen tolerance and cracking ability of the catalyst of the instantinvention would allow its use as a cracking catalyst for very highnitrogen polyaromatic stocks with little or no pretreatment.

DESCRIPTION OF PREFERRED EMBODIMENTS

The catalyst useful in this invention comprises a crystalline zeolitehaving an alpha value of between about 25 and 200 in intimate contactwith a nickel-tungsten hydrogenation component.

The crystalline zeolite is a member of a novel class of zeolites havinga silica to alumina ratio of at least 12, and a Constraint Index in theapproximate range of 1 to 12. The catalyst contains about 0.7 to about 7wt. % nickel and about 2.1 to about 21 wt. % tungsten, expressed asmetal, which functions as an hydrogenation component. The zeolite andhydrogenation component may be dispersed in a matrix such as alumina orclay. A particularly preferred zeolite is one having a crystallite sizeof less than about 5 microns.

The crystalline zeolites useful herein are members of a class ofzeolites exhibiting some unusual properties. These zeolites induceprofound transformation of aliphatic hydrocarbons to aromatichydrocarbons in commercially desirable yields and are generally highlyeffective in conversion reactions involving aromatic hydrocarbons.Although they have unusually low alumina contents, i.e., high silica toalumina mole ratios, they are very active even when the silica toalumina mole ratio exceeds 30. The activity is surprising since catalystactivity is generally attributed to framework aluminum atoms and cationsassociated with these aluminum atoms. These zeolites retain theircrystallinity for long periods in spite of the presence of steam at hightemperature which induces irreversible collapse of the framework ofother zeolites, e.g., of the X and A type.

An important characteristic of the crystal structure of this class ofzeolites is that it provides constrained access to, and egress from theintracrystalline free space by virtue of having a pore dimension greaterthan about 5 Angstroms and pore windows of about a size such as would beprovided by 10-membered rings of silicon atoms interconnected by oxygen.It is to be understood, of course, that these rings are those formed bythe regular disposition of the tetrahedra making up the anionicframework of the crystalline zeolite, the oxygen atoms themselves beingbonded to the silicon or aluminum atoms at the centers of thetetrahedra. Briefly, the preferred type zeolites useful in thisinvention possess, in combination: a silica to alumina mole ratio of atleast about 12; and a structure providing constrained access to theintercrystalline free space.

The silica to alumina mole ratio referred to may be determined byconventional analysis. This ratio is meant to represent, as closely aspossible, the ratio in the rigid anionic framework of the zeolitecrystal and to exclude aluminum in the binder or in cationic or otherform within the channels. Although zeolites with a silica to aluminamole ratio of at least 12 are useful, it is preferred to use zeoliteshaving higher ratios of at least about 30 and in some instances of atleast about 500. Such zeolites, after activation, acquire anintracrystalline sorption capacity for normal hexane which is greaterthan that for water, i.e., they exhibit "hydrophobic" properties. It isbelieved that this hydrophobic character is advantageous in the presentinvention.

The type zeolites useful in this invention freely sorb normal hexane andhave a pore dimension greater than about 5 Angstroms. In addition, thestructure must provide constrained access to larger molecules. It issometimes possible to judge from a known crystal structure whether suchconstrained access exists. For example, if the only pore windows in acrystal are formed by 8-membered rings of silicon and aluminum atoms,then access by molecules of larger cross-section than normal hexane isexcluded and the zeolite is not of the desired type. Windows of10-membered rings are preferred, although, in some instances, excessivepuckering or pore blockage may render these zeolites ineffective.Twelve-membered rings do not generally appear to offer sufficientconstraint to produce the advantageous conversions, although puckeredstructures exist such as TMA offretite which is a known effectivezeolite. Also, structures can be conceived, due to pore blockage orother cause, that may be operative.

Rather than attempt to judge from crystal structure whether or not azeolite possesses the necessary constrained access, a simpledetermination of the "constraint index" may be made by passingcontinuously a mixture of an equal weight of normal hexane and3-methylpentane over a sample of zeolite at atmospheric pressureaccording to the following procedure. A sample of the zeolite, in theform of pellets or extrudate, is crushed to a particle size about thatof coarse sand and mounted in a glass tube. Prior to testing, thezeolite is treated with a stream of air at 540° C. (1000° F.) for atleast 15 minutes. The zeolite is then flushed with helium and thetemperature adjusted between 290° C. (550° F.) and 510° C. (950° F.) togive an overall conversion between 10% and 60%. The mixture ofhydrocarbons is passed at a 1 liquid hourly space velocity (i.e., 1volume of liquid hydrocarbon per volume of zeolite per hour) over thezeolite with a helium dilution to give a helium to total hydrocarbonmole ratio of 4:1. After 20 minutes on stream, a sample of the effluentis taken and analyzed, most conveniently by gas chromatography, todetermine the fraction remaining unchanged for each of the twohydrocarbons.

The "constraint index" is calculated as follows: ##EQU1##

The constraint index approximates the ratio of the cracking rateconstants for the two hydrocarbons. Zeolites suitable for the presentinvention are those having a constraint index in the approximate rangeof 1 to 12. Constraint Index (CI) values for some typical zeolites are:

    ______________________________________                                        ZEOLITE                  C.I.                                                 ______________________________________                                        ZSM-5                    8.3                                                  ZSM-11                   8.7                                                  ZSM-12                   2                                                    ZSM-23                   9.1                                                  ZSM-35                   4.5                                                  ZSM-38                   2                                                    Clinoptilolite           3.4                                                  TMA Offretite            3.7                                                  Beta                     0.6                                                  ZSM-4                    0.5                                                  H-Zeolon                 0.4                                                  REY                      0.4                                                  Amorphous Silica-Alumina 0.6                                                  (non-zeolite)                                                                 Erionite                 38                                                   ______________________________________                                    

It is to be realized that the above constraint index values typicallycharacterize the specified zeolites but that such are the cumulativeresult of several variables used in determination and calculationthereof. Thus, for a given zeolite depending on the temperature employedwithin the aforenoted range of 290° C. (550° F.) to 510° C. (950° F.),with accompanying conversion between 10% and 60%, the constraint indexmay vary within the indicated approximate range of 1 to 12. Likewise,other variables such as the crystal size of the zeolite, the presence ofpossible occluded contaminants and binders intimately combined with thezeolite may affect the constraint index. It will accordingly beunderstood by those skilled in the art that the constraint index, asutilized herein, while affording a highly useful means forcharacterizing the zeolites of interest is approximate, taking intoconsideration the manner of its determination; with probability, in someinstances, of compounding variable extremes.

While the above experimental procedures will enable one to achieve thedesired overall conversion of 10 to 60% for most catalyst samples andrepresents preferred conditions, it may occasionally be necessary to usesomewhat more severe conditions for samples of very low activity, suchas those having a very high silica to alumina mole ratio. In thoseinstances, a temperature of up to about 540° C. (1000° F.) and a liquidhourly space velocity of less than one, such as 0.1 or less, can beemployed in order to achieve a minimum total conversion of about 10%.

The class of zeolites defined herein is exemplified by ZSM-5, ZSM-11,ZSM-12, ZSM-23, ZSM-35 and ZSM-38 and other similar materials. U.S. Pat.No. 3,702,886 describing and claiming ZSM-5 is incorporated herein byreference.

ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979, theentire contents of which is incorporated herein by reference.

ZSM-12 is more particularly described in U.S. Pat. No. 3,832,449, theentire contents of which is incorporated herein by reference.

ZSM-23 is more particularly described in U.S. Pat. No. 4,076,842, theentire contents of which is incorporated herein by reference.

ZSM-35 is more particularly described in U.S. Pat. No. 4,016,245, theentire contents of which is incorporated herein by reference.

ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859, theentire contents of which is incorporated herein by reference.

The specific zeolites described, when prepared in the presence oforganic cations, are catalytically inactive, possibly because theintracrystalline free space is occupied by organic cations from theforming solution. They may be activated by heating in an inertatmosphere at 540° C. (1000° F.) for one hour, for example, followed bybase exchange with ammonium salts followed by calcination at 540° C.(1000° F.) in air. The presence of organic cation in the formingsolution may not be absolutely essential to the formation of this typezeolite; however, the presence of these cations does appear to favor theformation of this special type catalyst by base exchange with ammoniumsalts followed by calcination in air at about 540° C. (1000° F.) forfrom about 15 minutes to about 24 hours.

Natural zeolites may sometimes be converted to this type zeolitecatalyst by various activation procedures and other treatments such asbase exchange, steaming, alumina extraction and calcination, incombinations. Natural minerals which may be so treated includeferrierite, brewsterite, stilbite, dachiardite, epistilbite, heulandite,and clinoptilolite. The preferred crystalline zeolites are ZSM-5,ZSM-11, ZSM-12, ZSM-23, ZSM-35 and ZSM-38 with ZSM-5 particularlypreferred.

In a preferred aspect of this invention, the zeolites hereof areselected as those having a crystal framework density, in the dryhydrogen form, of not substantially below about 1.6 grams per cubiccentimeter. It has been found that zeolites which satisfy all three ofthese criteria are most desired. Therefore, the preferred zeolites ofthis invention are those having a constraint index, as defined above ofabout 1 to about 12, a silica to alumina mole ratio of at least about 12and a dried crystal density of not less than about 1.6 grams per cubiccentimeter. The dry density for known structures may be calculated fromthe number of silicon plus aluminum atoms per 100 cubic Angstroms, asgiven, e.g., on Page 19 of the article on Zeolite Structure by W. M.Meier. This paper, the entire contents of which are incorporated hereinby reference, is included in "Proceedings of the Conference on MolecularSieves, London, April 1967", published by the Society of ChemicalIndustry, London, 1968. When the crystal structure is unknown, thecrystal framework density may be determined by classical pycnometertechniques. For example, it may be determined by immersing the dryhydrogen form of the zeolite in an organic solvent which is not sorbedby the crystal. It is possible that the unusual sustained activity andstability of this class of zeolites is associated with its high crystalanionic framework density of not less than about 1.6 grams per cubiccentimeter. This high density, of course, must be associated with arelative small amount of free space within the crystal, which might beexpected to result in more stable structures. This free space, however,is important as the locus of catalytic activity.

Crystal framework densities of some typical zeolites are:

    ______________________________________                                                        Void        Framework                                         Zeolite         Volume      Density                                           ______________________________________                                        Ferrierite      0.28 cc/cc  1.76 g/cc                                         Mordenite       .28         1.7                                               ZSM-5-11        .29         1.79                                              ZSM-12          --          1.8                                               ZSM-23          --          2.0                                               Dachiardite     .32         1.72                                              L               .32         1.61                                              Clinoptilolite  .34         1.71                                              Laumontite      .34         1.77                                              ZSM-4 (Omega)   .38         1.65                                              Heulandite      .39         1.69                                              P               .41         1.57                                              Offretite       .40         1.55                                              Levynite        .40         1.54                                              Erionite        .35         1.51                                              Gmelinite       .44         1.46                                              Chabazite       .47         1.45                                              A               .5          1.3                                               Y               .48         1.27                                              ______________________________________                                    

When synthesized in the alkali metal form, the zeolite is convenientlyconverted to the hydrogen form, generally by intermediate formation ofthe ammonium form as a result of ammoniun ion exchange and calcinationof ammonium form to yield the hydrogen form. In addition to the hydrogenform, other forms of the zeolite wherein the original alkali metal hasbeen reduced to less than about 1.5 percent by weight may be used. Thus,the original alkali metal of the zeolite or introduced hydrogen cationsmay be replaced by ion exchange with other suitable ions of Groups IB toVIII of the Periodic Table, including, by way of example, nickel,cadmium, copper, zinc, palladium, calcium or rare earth metals.

In practicing the desired method, it may be desirable to incorporate theabove-described crystalline zeolite in another material resistant to thetemperature and other conditions employed in the process. Such matrixmaterials include synthetic or naturally occurring substances as well asinorganic materials such as clay, silica and/or metal oxides. The lattermay be either naturally occurring or in the form of gelatinousprecipitates or gels including mixtures of silica and metal oxides.Naturally occurring clays, which can be composited with the zeoliteinclude those of the montmorillonite and kaolin families, which familiesinclude the sub-bentonites and the kaolins commonly known as Dixie,McNamee-Georgia and Florida clays or others in which the main mineralconstituent is halloysite, kaolinite, dickite, nacrite or anauxite. Suchclays can be used in a raw state as originally mined or initiallysubjected to calcination, acid treatment or chemical modification.

In addition to the foregoing materials, the zeolites employed herein maybe composited with a porous matrix material, such as alumina,silica-alumina, silica-magnesia, silica-zirconia, silica-thoria,silica-berylia, silica-titania as well as ternary compositions, such assilica-alumina-thoria, silica-alumina-zirconia, silica-alumina-magnesiaand silica-magnesia-zirconia. The matrix may be in the form of a cogel.The relative proporations of zeolite component and inorganic oxide gelmatrix may vary widely with the zeolite content ranging from betweenabout 1 to about 99 percent by weight and more usually in the range ofabout 5 to about 80 percent by weight of the composite.

The degree of zeolite acid activity of zeolite catalysts can be measuredand compared by means of "alpha value" (α). The alpha value reflects therelative activity of the catalyst with respect to a high activitysilica-alumina cracking catalyst. To determine the alpha value as suchterm is used herein, n-hexane conversion is determined at a suitabletemperature between about 290° C..540° C. (550° F.-1000° F.), preferablyat 540° C. (1000° F.). Conversion is varied by variation in spacevelocity such that a conversion level of up to about 60 percent ofn-hexane is obtained and converted to a rate constant per unit volume ofzeolite and compared with that of silica-alumina catalyst which isnormalized to a reference activity of 540° C. (1000° F.). Catalyticactivity of the catalysts are expressed as multiple of this standard,i.e. the silica-alumina standard. The silica-alumina reference catalystcontains about 10 weight percent Al₂ O₃ and the remainder SiO₂. Thismethod of determining alpha, modified as described above, is more fullydescribed in the Journal of Catalysis, Vol. VI, pages 278-287, 1966. Thecatalyst of the present invention has a zeolite catalyst activity (asmeasured without the presence of the hydrogenation component) in termsof alpha value of between about 25 and 200, and preferably of betweenabout 50 and 125.

The attainment of a desired alpha value for a zeolite can beaccomplished by a number of means, or a combination of such means. Onemethod to reduce alpha value of an active (acid) form of the zeolite isby steaming. Alternatively, reduction of acid activity and hence alphavalue of a zeolite can be reduced by ion exchange with sodium or otheralkali metal. Alpha value will also be reduced by increasing the silicato alumina mole ratio. In order to obtain a particular alpha value itmay be desirable in some instances to use a zeolite with a high silicato alumina mole ratio in conjunction with steam treatment.

The nickel-tungsten hydrogenation component and the zeolite component ofthe catalyst of the present invention are in intimate contact with oneanother. They are not merely mixed together. One method in which suchintimate contact can be attained is by impregnation of the hydrogenationcomponent. Pellets of the hydrogen form zeolite, for example, may beimpregnated with aqueous solutions of ammonium metatungstate and nickelnitrate to associate the zeolite with the hydrogenation component.Impregnation can occur during one course of making catalyst extrudate,or after the extrudate is formed. The nickel and tungsten can be addedtogether during such impregnation, or alternatively the tungsten can beadded in the muller, with the nickel added after the extrudate isformed.

Feedstocks for this invention are polynuclear aromatic containingliquids derived from such sources as petroleum, coal, shale oil, tarsands, etc. Particularly suitable feedstocks for the present inventioncomprise refractory stocks such as FCC cycle oil and also the productsof coal liquefaction processes.

Highly aromatic petroleum liquids are suitable feedstocks for thisinvention. Heavy aromatic, high sulfur content crudes make up anincreasing fraction of today's refinery feeds. This trend towards lessdesirable refinery feed is very likely to continue in the near future.Furthermore, refinery by-product liquids such as FCC clarified slurryoil and FCC cycle oil can be hydrocracked in accordance with thisinvention to produce significant amounts of gasoline and diesel fuel.

Products from the liquefaction of coal are generally highly aromatic andthus would be prime feedstocks for the novel hydrocracking process ofthe present invention. Coal is liquefied by exposing it to hydrogen gasor a hydrogen-bearing solvent under pressure and, in many processes, inthe presence of a catalyst. Temperatures are generally kept below 480°C. (900° F.) so that the hydrocarbons are not converted to coke andgaseous products. Alternatively, coal can be destructively distilled byheating in such a way that its volatile components are given off and canthen be condensed as a liquid. The net result is an increasedhydrogen/carbon ratio in the liquid products. Hydrogen is generated bygasifying a portion of the coal, or of a coal residue in most schemes,and this is a substantial portion of the cost of liquefaction. Sulfurcontent of the coal is also an important constraint, since hydrogen isalso needed to remove this contaminant (as hydrogen sulfide gas), inproportion to the amount of sulfur present. In theory, it is somewhateasier and cheaper to make a heavy oil from coal suitable for a boilerfuel than a synthetic crude oil that can be refined to gasoline, sincethe crude oil product requires adding about twice as muchhydrogen--between 5 and 10 percent of the coal's weight. Boiler fuelsmay also have an economic advantage in that they would supply aregulated market--the electric utility industry that now generates about30 percent of its power with oil and natural gas--making commercialintroduction somewhat easier.

The three direct general processes for converting coals to liquid fuelsare: catalyzed hydrogenation, staged pyrolysis, and solvent refining.Each of these processes results in the production of a coal liquid whichcontains a variety of desirable and undesirable components. Thedesirable coal liquids are the oils (saturated and aromatichydrocarbons) and the resins.

The undesirable species are the asphaltenes and the carbenes (highmolecular weight highly aromatic solids) and the carboids (polymerizedcoke-like materials). The undesirable elements are the metals, sulfur,nitrogen, and oxygen which are generally present in higher concentrationin the asphaltene and carboid fractions. Under hydrogenolysisconditions, the conversion of coal to oil has been suggested to proceedvia the following sequence: Coal→Asphaltene→Oil. Therefore, asphaltenegeneration and elimination are of great importance in the liquefactionprocess.

One example of a typical coal liquefaction process is the SolventRefined Coal (SRC) process, which is a method of dissolving coal toremove its ash, reduce its sulfur content and lower its averagemolecular weight. Pulverized coal is mixed with a solvent and hydrogenand heated until most of it dissolves. Gases including hydrogen sulfideare removed, as are ash and other undissolved solids. A fraction of theremaining liquid is recycled as the solvent, and the rest is product, alow-sulfur boiler fuel that is solid at room temperature but meltsreadily at about 190° C. (375° F.). It is the light organic liquidderived from the Solvent Refined Coal (SRC) process that can be afeedstock for this invention.

Another coal liquefaction process is the H-Coal process. In thisprocess, coal is converted to oil by direct hydrogenation. The sequenceof processing steps is essentially the same as in solvent refiningexcept that the mixture of finely ground coal, recycle oil, and hydrogenare reacted in the presence of a catalyst. The process can produceeither synthetic crude oil or, by lowering the reaction temperature andadding less hydrogen, a heavy-oil boiler fuel. The synthoil process issimilar to H-Coal in that it is also a catalytic process.

Still another coal liquefaction process is the Donor Solvent process.This process differs from H-Coal in that hydrogenation of the coal iscarried out indirectly, through a solvent that transfers hydrogen to thecoal while extracting a liquid product.

In comparison with conventional petroleum feedstocks and residua coalliquids generally exhibit slightly higher carbon content, butsignificantly lower hydrogen content. Recent data suggests both a higherdegree of aromaticity and a more highly condensed ring structure forcoal liquids than for conventional petroleum type liquids.

A more striking difference between the coal liquids and conventionalpetroleum type liquids is the heteroatom content. Nitrogen and oxygenlevels in coal liquids are generally much higher than in petroleum, butsulfur is somewhat lower. Furthermore, 40-70 wt. % of the nitrogen incoal liquids is basic in character compared to 25-30 wt. % for typicalconventional petroleum stocks.

The aromaticity of a particular feedstock can be expressed as "% C_(A)". The "% C_(A) " is defined as the percent of carbon atoms which arepresent in aromatic rings based on the total amount of carbon atoms andis given by the formula: ##EQU2## The % C_(A) for representativecompounds are as follows:

    ______________________________________                                        Benzene                                                                                  ##STR1##       % C.sub.A = 100%                                    Toluene                                                                                  ##STR2##       % C.sub.A = 85.7%                                   Xylene                                                                                   ##STR3##       % C.sub.A = 75%                                     ______________________________________                                    

Liquid feeds that would be amenable to this invention would have anaromaticity as expressed in % C_(A) in a range between about 30% and100% and preferably between about 40% and 100%.

Aromaticity is a function of boiling point. This is clearly shown inTable 1 which gives properties, including % C_(A), for various petroleumcomponents.

Table 2 gives aromaticities for various coal liquids and petroleumresidua. It can be seen from Table 2 that the % C_(A) for coal derivedliquids range from between about 50% and 80%, while the % C_(A) forpetroleum residua ranges from between about 20% and 35%.

The aromatic feedstock of this invention must be further characterizedby having a majority of its aromaticity in "polynuclear aromatics".Polynuclear aromatics are aromatic compounds having three or moreconnected aromatic rings, such as anthracene, phenanthrene, chrysene,etc.

                                      TABLE 1                                     __________________________________________________________________________    AROMATICITY OF PETROLEUM COMPONENTS                                                        FCC  FCC   FCC   Coker                                                                              Coker                                                   Light                                                                              Light Clarified                                                                           Light                                                                              Heavy                                                   Gasoline                                                                           Cycle Oil                                                                           Slurry Oil                                                                          Gas Oil                                                                            Gas Oil                                    __________________________________________________________________________    Gravity, °API                                                                       47.9 17.4  0.3   33.1 21.6                                       Hydrogen, Wt. %                                                                            12.68                                                                              9.80  7.97  12.74                                                                              11.28                                      Nitrogen, Wt. %                                                                            0.031                                                                              0.25  0.41  0.30 0.76                                       Aromaticity, % C.sub.A                                                                     36   54    70    23   38                                         Distillation (D-2887), °F.                                             5%           79   398   576   346  469                                        50%          274  523   727   459  597                                        95%          404  677   863   543  686                                        __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                        AROMATICITIES OF COAL LIQUIDS AND PETROLEUM                                   RESIDUA DETERMINED BY C13 NMR SPECTROSCOPY                                                  % C.sub.A C/H                                                                 (Atom %)  (Atom Ratio)                                          ______________________________________                                        SRC type I from 77          1.29                                              Illinois No. 6 Coal                                                           S'RC Recycle Solvent                                                                          70          0.970                                             Synthoil from   61          0.922                                             Illinois No. 6 Coal                                                           H-Coal from Illinois                                                                          63          0.940                                             No. 6 Coal (fuel oil                                                          mode)                                                                         Petroleum No. 6 24          0.647                                             Fuel Oil                                                                      Mid-Continent   19          0.600                                             Vacuum Residuum                                                               West Texas Sour 34          0.706                                             Vacuum Residuum                                                               ______________________________________                                    

Large amounts of sulfur, nitrogen and oxygen (high heteroatom content)generally decrease the overall efficiency of processing catalysts.Therefore the removal of such contaminants or the ability to toleratesame is very important in the production of high quality fuels from theaforesaid feedstocks. Whereas hydrocracking typically involves both apretreating catalyst to remove heteroatoms such as nitrogen and sulfurand a cracking catalyst to produce valuable liquid fuels, the catalystof the instant invention can in many instances perform both functions.Thus the need for pretreatment may be reduced, or totally eliminated.

The catalyst utilized in the instant invention is particularly nitrogensensitive and acts to reduce nitrogen and sulfur contents whileincreasing hydrogen content and saturating a substantial amount ofpolynuclear aromatics. CCR reduction is also possible with thiscatalyst. The novel process of this invention will also afford operationat much lower pressures required for conventional hydrocracking, e.g.operation at about 74 kg/cm² gage (1050 psig) rather than 106 kg./cm²gage (1500 psig) with concomitant lower hydrogen consumption while stillproducing significant amounts of gasoline and high quality diesel fuels.

Hydrocracking in accordance with the present invention is conducted at atemperature of between about 205° C. (400° F.) and 510° C. (950° F.)preferably between about 260° C. (500° F.) and 425° C. (800° F.), apressure of between about 7 kg./cm² gage (100 psig) and 141 kg./cm² gage(2000 psig) preferably between about 28 kg./cm² gage (400 psig) and 105kg./cm² gage (1500 psig), a liquid hourly space velocity (LHSV), i.e.the liquid volume of hydrocarbon per hour per volume of catalyst, ofbetween about 0.1 and 10, and a molar ratio of hydrogen to hydrocarboncharge of between about 2 and 80, preferably between about 5 and 50.

The process of this invention may be carried out in equipment suitablefor catalytic operations. The process may be operated batchwise. It ispreferable, however, and generally more feasible, to operatecontinuously. Accordingly, the process is adapted to operations using afixed bed of catalyst. Also the process can be operated using a movingbed of catalyst wherein the hydrocarbon flow may be concurrent orcountercurrent to the catalyst flow. A fluid type of operation may alsobe employed with the catalyst described herein. After hydrocracking theresulting products may be suitable separated from the remainingcomponents by conventional means such as adsorption, distillation, etc.Also the catalyst, after use over an extended period of time, may beregenerated with hydrogen or in accordance with conventional proceduresby burning off carbonaceous deposits from the surface of the catalyst inan oxygen containing atmosphere under the conditions of elevatedtemperature.

The following examples will serve to illustrate the invention withoutlimiting same.

EXAMPLE 1

This example illustrates the preparation of a catalyst useful in thisinvention.

A mixture of 65 wt. % ZSM-5 having a crystallite size of less than 0.05microns and 35 wt. % alumina on an anhydrous basis was extruded to form1/16 inch pellets. The pellets were calcined at 540° C. (1000° F.) innitrogen, ammonium exchanged, and then calcined in air.

100 grams of the air-calcined extrudate was impregnated with 13.35 gramsof ammonium matatungstate (73.3% W) in 60 cc of water, followed bydrying at 240° C. and calcination in air at 540° C. (1000° F.). Theextrudate was then impregnated with 15.06 grams of nickel hexahydrate in60 cc of water, and the wet pellets dried and again calcined in air at540° C. (1000° F.).

The final catalyst had a calculated nickel content of about 1.7 wt. % asNiO, a calculated tungsten content of about 10.5 wt. % as WO₃, 57.1 wt.% ZSM-5 and 30.7 wt. % alumina.

EXAMPLES 2-4

In examples 2-3, an FCC Light Cycle Oil chargestock was contacted withthe catalyst of Example 1. In Example 4, the aforesaid chargestock wascontacted with a commercial CHD catalyst. The results for Examples 2-4are given in Table 3. The properties of the FCC Light Cycle OilChargestock are as follows:

    ______________________________________                                        Gravity, °API 16.1                                                     Sulfur, wt. %        3.19                                                     Hydrogen, wt. %      9.89                                                     Nitrogen, wt. %      .0705                                                    Wt. % Compound Type Analysis (400.sup.+)                                      Paraffins            17.3                                                     Naphthenes           13.3                                                     Mono Aromatics       10.0                                                     Poly Aromatics       59.4                                                     ______________________________________                                    

In comparing the results of the catalyst utilized in this invention(Examples 2-3) to a commercial CHD catalyst (Example 4), it is readilyseen that the catalyst utilized in the present invention exhibitssuperior denitrogenation and desulfurization capabilities and a muchgreater conversion of polynuclear aromatics.

The results for Example 2 show a nitrogen reduction of from 705 ppm to14 ppm, a sulfur reduction of from 3.19 wt. % to 0.12 wt. %, anincreased hydrogen content from 9.89 wt. % to 12.12 wt. %, a polynucleararomatics conversion to saturates, monoaromatics and gasoline of about90% and a gasoline make of 26 vol. % on a single pass.

                  TABLE 3                                                         ______________________________________                                        HYDROCRACKING OF AN FCC LIGHT CYCLE OIL                                                       EXAM-  EXAM-    EXAM-                                                         PLE    PLE      PLE                                                           2      3        4                                             ______________________________________                                        Days on Stream    1.1      1.7      --                                        Space velocity, LHSV                                                                            0.49     0.89     3.0                                       Temp., °F. 707      694      600                                       Pressure, psig H.sub.2                                                                          1500     600      425                                       H.sub. 2 Circulation, SCF/B                                                                     9299     2936     1257                                      Yields, Wt. %                                                                 H.sub.2 S + NH.sub.3                                                                            3.35     2.96     2.35                                      C.sub.1 -C.sub.3  2.56     4.89     .01                                       C.sub.4           3.42     3.17     2.0                                       nC.sub.4          1.79     1.6      0.0                                       C.sub.5.sup.+     93.24    90.35    98.25                                     Yields, Vol. %                                                                iC.sub.4          2.39     2.54     0                                         C.sub.5 -180° F., Lt.Naphtha                                                             12       8        0                                         180° F.-390° F., Hvy Naphtha                                                      14       8        0                                         iC.sub.4 + C.sub. 5.sup.+ yield                                                                 103.5    97.0     100.98                                    H.sub.2 Consumption, SCF/B                                                                      1642     875      384                                       Product Properties                                                            Gravity, °API                                                                            32.7     23.8     20.1                                      Sulfur, wt. %     0.12     .49      1.01                                      Hydrogen, wt. %   12.12    10.75    10.54                                     Nitrogen, wt. %   .0014    .0386    .0601                                     % WT Cmpd Type Anal. (400+)                                                   Paraffins         9.3      8.2      19.4                                      Naphthenes        21.0     11.3     11.9                                      Mono Aromatics    28.7     23.6     24.3                                      Poly Aromatics    6.0      29.9     44.4                                      Total 400.sup.-  Conversion                                                                     35.0     27.0     --                                        Selectivities                                                                 (Wt. C.sub.1 -C.sub.3)/Wt. Conv.                                                                7.31                                                        Wt. nC.sub.4 /wt. Conv.                                                                         5.09                                                        Total             12.4                                                        ______________________________________                                    

What is claimed is:
 1. A process for hydrocracking a polynucleararomatic containing feedstock having a %C_(A) within the range of fromabout 30% to about 100% which comprises contacting said feedstock underconversion conditions including a temperature of between about 400° F.and 950° F., a pressure of between about 100 psig and 2000 psig, a LHSVof between about 0.1 and 10, and a molar ratio of hydrogen tohydrocarbon charge of between about 2 and 80 with a catalyst comprisingone or more members of a class of zeolites characterized by a silica toalumina mole ratio of at least 12, a constraint index in the approximaterange of 1 to 12 and an alpha value of between about 25 and 200 andwherein said zeolite is in intimate contact with a nickel-tungstenhydrogenation component.
 2. The process of claim 1 wherein said zeoliteis ZSM-5, ZSM-11, ZSM-12, ZSM-23, ZSM-35, or ZSM-38.
 3. The process ofclaim 2 wherein said zeolite is ZSM-5.
 4. The process of claim 1 whereinsaid zeolite has a crystallite size of less than about 5 microns.
 5. Theprocess of claim 1 wherein said feedstock is FCC light cycle oil.
 6. Theprocess of claim 1 wherein said alpha value is between about 50 and 125.7. The process of claim 1 wherein said intimate contact is attained byimpregnation.
 8. The process of claim 1 wherein said conversionconditions include a temperature of between about 500° F. and 800° F., apressure of between about 400 psig and 1500 psig, a LHSV of betweenabout 0.1 and 10, and a molar ratio of hydrogen to hydrocarbon charge ofbetween about 5 and
 50. 9. The process of claim 1 wherein saidhydrogenation component consists of about 0.7 to about 7 wt. % nickeland about 2.1 to about 21 wt. % tungsten expressed as metal based onsaid catalyst.
 10. The process of claim 1 wherein said zeolite iscontained in an alumina matrix.